The invention relates to a method for optical chassis measurement of motor vehicles at a testing site, in which, with at least two imaging devices of an imaging system that are associated with one another in position and location, or other sensors detecting the surface geometry of another measurement device detecting the surface geometry, an orientation of this arrangement or arrangements is made with respect to the testing site with the aid of reference characteristics located at the testing site, and in an evaluation device, on the basis of the orientation data and/or association data as well as measurement region data obtained, an evaluation is made for determining chassis data taking the auto body characteristics into account, and to an apparatus for performing the method.
One such method for optical chassis measurement, namely for measuring wheel and axial geometric data, in particular, such as toe-in and camber, is disclosed in German Patent Disclosure DE 100 50 653 A1. This reference also makes more-detailed remarks on various ways of proceeding to reference the measurement device with regard to the vertical direction of the measuring station (testing site) and the mutual association of the recording locations (position and direction) of the imaging devices with respect to one another. The referencing, hereinafter also called orientation, is done on the basis of reference characteristics in the measurement chamber of the testing site, so that a vertical plane to the roadway plane, for instance, and the travel axis can both be determined from the motion of the measurement characteristics in the vehicle, from which in turn the wheel axle angle of a wheel can be determined. It is also disclosed for instance for the optical measuring device to be referenced during travel past it, with initially unknown reference characteristics used for the evaluation device. Determining the chassis data in this known method, that is, the wheel and/or axle geometry data, is then performed including wheel characteristics and optionally auto body characteristics, and the measurement can be done with the vehicle at a standstill or alternatively as it travels past.
Similar methods for determining the wheel and/or axle geometry of motor vehicles are disclosed in German Patent Disclosure DE 197 57 763 A1 and European Patent Disclosure EP 1 042 643 B1. In this case, a separate reference characteristic array is positioned at the testing site. In German Patent Disclosure DE 199 34 864 A1 as well, an optical measuring method, developed on the basis of these known methods, for the wheel and/or axle geometry is disclosed. Although with these methods and apparatuses it was possible to reduce the complexity of the chassis measurement considerably, there are still some disadvantages, namely the adaptability in axial measurement to different wheelbases ranging from small cars to the most expensive vehicles in a stretch version, since then large dimensions are needed for the supporting frame of the reference characteristics, making this impractical for use on a hydraulic lift. Moreover, measurement characteristics of the vehicle may be concealed, resulting in measurement imprecision. Other disadvantages that can be named are the risk of injury for mechanics, the risk of damage to vehicles during the measurement from scratches or deformations of the auto body, limitation in terms of the flexibility of using the occupied space in the workshop, and the risk of deformation of the supporting frame with a resultant loss of precision. In the reference characteristic array that is suspended in pendulum fashion, it is inconvenient to operate the equipment if the pendulum arrangement is used in mobile fashion before the measurement, among other reasons because it is necessary to wait for the terminal position of the pendulum. Moreover, the use of the pendulum results in an absolute leveling of the measuring station because of the direction of gravity detected, which in reality is only present in exceptional cases, so that the typical auto body coordinate system described in DE 199 34 864 A1 as well is referred to the absolute leveling because of the transformation of the direction of gravity detected with the pendulum. The camber ascertained in the process at the observed wheel is therefore likewise referred to the absolute leveling, rather than to the actually existing global measuring station coordinate system.
In European Patent Disclosure EP 0 895 056 A2, it is proposed, for an axle measurement, to use structures present anyway on the vehicle wheel, namely in particular the bead of the rim. For determining the 3D position and location of the wheel plane, the location of the plane of the bead of the rim is derived from the two images of two imaging devices, and abrupt transitions in gray values are evaluated. However, for orientation of the imaging devices and/or measuring units, no further details are provided.
High-precision chassis measurement, in particular also the determination of the wheel and axle geometry of vehicles, is becoming more and more important with the increasingly improved technology of chassis. New and more finely tuned capabilities for adjusting toe-in and camber of the individual wheels require a measurement device with correspondingly high precision, if at all possible without being affected by the conditions of the particular testing site. The orientation of the imaging devices and measuring units containing them is of essential importance.